Electrostatic Force Microscopy And Kelvin Probe Force Microscopy

Abstract

Abstract Studying electrostatic and electronic surface properties such as work function (WF) or local charge phenomena is of high importance not only in surface physics and chemistry, but also in materials science and related fields. Electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) give access to these properties providing resolution on the nanometer lateral length scale, which explains their large success in science. Both techniques are based on noncontact atomic force microscopy (nc‐AFM) and use an applied bias voltage to excite a cantilever oscillation, whose amplitude depends on the electrostatic force interaction between the AFM tip and the sample. The EFM directly measures this electrostatic force; however, KPFM uses a compensation technique to allow quantitative determination of the local surface potential. A commonly used method is to apply a static (dc) and alternating (ac) voltage between the tip and surface such that the electrostatic tip–surface interaction is modulated, which greatly helps in detecting small electrostatic forces. Two working modes can be used: the amplitude modulation mode is directly sensitive to the electrostatic force, while the frequency modulation mode detects the electrostatic force gradient. The methods can be applied to a variety of samples. For instance, on conducting surfaces such as metal and semiconductor surfaces the contact potential difference (CPD) is measured, which represents the WF difference between the tip and sample. An image of the CPD reflects variations of the surface WF at the nanometer scale—an important surface property for any field of research. On the other hand, information about the local charge or dipole distribution is also obtained, which is of utmost importance if insulators are considered. This article gives an introduction into the principles and practical aspects of the EFM and KPFM techniques and provides a number of application examples.